When any communication command furnished in serial data is to be multiplexed into horizontal blanking portions of video data (e.g., 8-bit parallel data), the serial communication command is first converted conventionally to parallel data reaching the CPU (central processing unit) or the like. It is in the form of parallel data that the communication command is multiplexed into the horizontal blanking period of video data.
If the transmission rate of serial communication command data is lower than the horizontal blanking rate (about 15 kHz), the conventional method above necessarily entails a delay equivalent to the serial-parallel conversion time for multiplexing.
For example, consider 11-bit serial communication command data composed of a start bit (1 bit), data (8 bits), a parity bit (1 bit) and a stop bit (1 bit). In such a case, to perform the conventional serial-parallel conversion requires waiting for the entire 11-bit data to be received. If the rate of serial communication command data is 9,600 bps, the delay amounts to approximately 17 horizontal periods. Where the data is to be multiplexed into horizontal blanking portions in each of the 17 horizontal periods, complicated control procedures are needed illustratively to determine which blanking portion is to have the data multiplexed therein and which portion is not to.
It is therefore an object of the present invention to provide an apparatus and a method for multiplexing serial data involving little data delay and without complicated control procedures for multiplexing.